Evaluation of a Cell-Adapted Live Attenuated African Swine Fever Virus Thai-Strain Vaccine Candidate: Highlighting Enhanced Virulence Risk in Co-Infected Pigs

African swine fever (ASF) is a devastating disease affecting the swine industry globally. Development of safe and effective vaccines is an urgent need. This study aimed to evaluate, caASFV001-MA52, a cell-adapted ASFV strain derived from serial passaging in MA-104 cells, as a promising live-attenuated vaccine (LAV) candidate against virulent ASFV infection.

Seven-week-old, crossbred pigs were immunized with caASFV001-MA52 (at a dose of 10⁵ TCID₅₀) and subsequently challenged with a lethal dose of virulent ASFV. Vaccine efficacy was measured through clinical monitoring, immunological and virological analyses, and pathological assessments of tissue protection and viral load reduction. Safety was critically assessed, particularly regarding its profile in animals with concurrent endemic porcine infections, including PCV, PRRSV and S. suis.

caASFV001-MA52 exhibits partial protection (70-80%) against the lethal challenge. Vaccinated and challenged survivors exhibited reduced viral loads and significantly alleviated pathological lesions compared to controls. Safety evaluations revealed that the vaccine's profile is susceptible to concurrent infection. Pigs co-infected with endemic porcine pathogens showed increased virulence and mortality following vaccination. Although vaccination temporarily reactivated latent viral infections (PCV2, PCV3, and PRRSV), most surviving pigs effectively controlled and eliminated these co-infections.

The caASFV001-MA52 strain demonstrates promising immunogenicity and protection against lethal challenges, supporting its continued development as an LAV candidate. However, the observed safety concerns regarding concurrent infections emphasize the critical need for veterinary health surveillance during its future practical application.